Methods for the mechanical, catalytic or chemical treatment of the combustion waste gases of furnaces, waste incinerators or other industrial plants, gas turbines or engines are combined under the general term exhaust gas treatment. An exhaust gas treatment carried out according to the state of the art, optionally combined with further measures affecting the mixture formation or combustion, reduces the pollutant output of conventional internal combustion engines.
While so-called regulated three-way catalytic converters have been part of the legally required minimum equipment for participation in public road traffic for, e.g., motor vehicles with spark ignition engines for a long time in numerous states, the state of the art provided for only insufficient exhaust gas treatment for the exhaust gases of comparable diesel engines over many years, because the higher air-to-fuel ratios of this engine variant compared to spark ignition engines imposes special functional requirements on corresponding means. In addition, the load of the diesel engine is set only by adapting the quantity of injected fuel, unlike in case of a spark ignition engine, in which it is set by adapting the total volume of the air-fuel ratio. Consequently, the particulate emission can be affected only slightly by limiting the fuel supply in case of diesel engines of this class.
The strict limitation of such particulate emissions required by law is therefore achieved in the state of the art with soot filters, which are also called soot particle filters (SPF) according to the composition of the particles to be filtered or diesel particle filters (DPF) according to the origin of these particulate emissions and aim to achieve a reduction of the concentration of these combustion residues remaining in the discharged exhaust gas stream. A catalytic converter (cat), which, combined with a diesel engine, often corresponds to the usual principles of action of a so-called oxidation catalytic converter or of the selective catalytic reduction (SCR), is also used for reducing emission of pollutants. Assembly units comprising such and other filters, catalytic converters or thermal reactors shall be combined under the term “exhaust gas treatment device” in the following descriptions.
Special attention is paid above all to the so-called pressure loss or pressure drop of the different exhaust gas treatment elements besides further fluidic operating parameters. In case of filters of this class, such a pressure difference arises already from the inherent flow resistance coefficient of the filter body in the original state thereof, which is due to the design and the material. However, the continual embedding and deposition of the solids separated from the exhaust gas stream, for example, in the form of a so-called filter cake, often increases the flow resistance considerably during the ongoing operation of the exhaust gas treatment device, so that the counterpressure exerted by the filter increases steadily as well. The rising counterpressure leads, in turn, to a steady reduction of the volume flow through the entire means.